The effect of vitronectin on platelet aggregation has been investigate
d. Vitronectin inhibited both thrombin- and ADP-induced platelet aggre
gation in a dose-dependent manner. A monoclonal antibody (MoAb) to vit
ronectin increased thrombin-induced platelet aggregation. This effect
of the MoAb was not mediated via the platelet Fc-receptor, suggesting
that the antibody directly counteracted the inhibitory effect of vitro
nectin on platelet aggregation. Like some other adhesive proteins such
as fibrinogen, fibronectin, and von Willebrand factor, vitronectin co
ntains the amino-acid sequence Arg-Gly-Asp (RGD) which enables binding
to the platelet membrane glycoprotein complex IIb/IIIa (GPIIb/IIIa).
The results of this study indicate that vitronectin can modulate the f
unction of fibrinogen on platelet aggregation by interfering with the
binding of fibrinogen to GPIIb/IIIa in activated platelets.